Wobble plate type pump and motor transmission



May 16, 1961 K. BAUER 2,984,070

WOBBLE PLATE TYPE PUMP AND MOTOR TRANSMISSION Original Filed Oct. 19, 1950 2 Sheets-Sheet 1 F/GJ INVENTOR. KARL BAUER May 16, 1961 K. BAUER 2,984,070

WOBBLE PLATE TYPE PUMP AND MOTOR TRANSMISSION Original Filed Oct. 19, 1950 2 Sheets-Sheet 2 T will I\ IN V EN TOR.

United States Patent WOBBLE PLATE TYPE PUMP A'ND MOTOR TRANSMISSION Karl Bauer, Kainsbacherstrasse 2, Numberg-Laufamholz, Germany Application Feb. 17, 1955, Ser. No. 488,898, new Patent No. 2,862,456, dated Dec. 2, 1958, which is a contmuation of abandoned application Ser. No. 190,942, Oct. 19, 1950. Divided and this application Nov. 24, 1958, Ser. No. 775,761

Claims priority, application Germany Oct. 19, 1949 8 Claims. (Cl. 60-53) The present invention relates to a wobble plate type pump and motor transmission, and more particularly to an arrangement for reducing the friction between the parts of the transmission.

The present application is a divisional application of my co-pending application Serial No. 488,898 entitled Rotary Wobble Plate Type Pump or Motor, filed on February 17, 1955, now Patent No. 2,862,456, issued December 2, 195 8, which application is a continuation of my abandoned application Serial No. 190,942, filed October 19, 1950.

In known wobble plate type transmissions considerable friction exists between the moving parts of the transmission, and it is the main object of the present invention to overcome this disadvantage.

Another object of the present invention is to provide a hydraulic transmission in which the effective hydraulic forces compensate each other.

Another object of the present invention is to take up the hydraulic forces acting in opposite directions on the two wobble plates of the transmission by a common shaft.

A further object of the present invention is the provision of continuous passages between the bearing faces of the two wobble plates, such passages communicating with the working chambers of the cylinders of the pump and motor.

A further object of the present invention is to provide between the cylinder blocks of the pump and motor, a valve member which is of substantially smaller diameter than the cylinder blocks so that the frictional torque is reduced.

A further object of the present invention is to resiliently urge one of the cylinder blocks against the valve member.

An additional object of the present invention is to regulate one of the wobble plates by servo-motor means.

With these objects in view, the present invention mainly consists in a hydraulic pump and motor transmission comprising, in combination, supporting means; a pair of coaxial cylinder blocks, one of said cylinder blocks being mounted for rotation and the other of said cylinder blocks being fixedly mounted in said supporting means, said cylinder blocks having confronting inner end faces, each of said cylinder blocks being formed with a set of cylinder bores having ports opening on said end faces respectively, each cylinder block having a central opening; piston means including a piston in each of said cylinder bores and a piston rod, said pistons forming in the associated cylinder bores working chambers communicating with said ports; drive shaft means connected to said rotary cylinder block and passing through said central openings of said cylinder. blocks; a valve member secured to said shaft means for rotation therewith and being located between said confronting inner end faces and having sealing faces slidably engaging said inner end faces, said valve member being formed with conduits passing 2,984,070 Patented May 16, 1961 therethrough and opening on said sealing faces in ports cooperating with said ports of said cylinder blocks during relative turning movement between said valve member and cylinder blocks; a pair of wobble plate means secured to said shaft means for rotation therewith, said Wobble plate means being located on opposite sides of said pair of cylinder blocks and having bearing surfaces facing toward the same; and a pair of bearing members mounted on said wobble plate means, respectively, for rotation relative thereto and having bearing surfaces slidably engaged by said bearing surfaces of said wobble plate means, and pressure pockets receiving the piston rods.

In accordance with the present invention, the pistons, piston rods and bearing members are formed with passages connecting the pair of cooperating bearing surfaces between each wobble plate means and each bearing member to the working chambers so that fluid communication is established between the pairs of bearing surfaces through the passages, working chambers and conduits in the valve member. Consequently, the fluid pressure produced in the working chambers acts in opposite directions on the wobble plate means and is taken up by the portion of the shaft means located between the wobble plate means whereby the friction between the bearing surfaces and said inner end faces and sealing faces is reduced.

Preferably, the valve member has circular sealing faces having an area smaller than the inner end faces of the cylinder blocks, and the working chambers of the cylinders are connected with the ports of the valve member by passages which are inclined to the axis of the transmis- SlOl'l.

In a preferred embodiment of the present invention, the rotary cylinder block is shiftable in axial direction, and is urged by a spring against the valve member.

Preferably, the valve member is formed with a passage connecting the conduits therein, and control valve means are located in this passage.

In accordance with the preferred embodiment of the present invention, the total area of the wobble plate means on which fluid pressure acts is equal to the total cross sectional area of the pistons and Working chambers on which the hydraulic pressure acts since in this manner, the friction between the sliding surfaces is reduced to a minimum.

An intermediate bearing disc is inserted between each wobble plate andbearing member and is formed with hydraulic pressure spaces adjacent the wobble plates which are connected by the passages through the piston rods to the working chambers of the cylinders. The sum of the areas of the pressure spaces corresponds to the sum of the cross sectional areas of the cylinder working chambers and pistons.

The pressure pockets and pressure spaces are effective to relieve ball heads of the piston rods from the piston pressure since the effective cross section of the ball head is also equal to the piston areas. The cylinder head pressure is relieved by the control valve member and the hydraulic forces in a direction from the control means to the remaining part of the cylinder end faces of the cylinder end plates are approximately equal to the effective hydraulic forces acting on the cylinder end plates in a direction from the working chambers of the cylinders.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which;

Figure l is a longitudinal sectional view of thetransmission;

Figure 2 is a cross section taken on line 22 of Figure Figure 3 is'a cross section taken on line 33 of Figure 1; and

Figure 4 is a cross section taken on line 4-4 of Figure The drive shaft 1, which is journalled in ball bearings- 8 in a supporting means, shown to be a cover plate 6, drives a rotary pump cylinder block 4 and also by means of a coupling roller 16 guided in a track 17 parallel to the shaft, actuates an end bearing ring member 15 which is part of the pump assembly. The end bearing ring member 15 thus rotates at the same speed as the rotary pump cylinder block 4 and the driving shaft 1. A wobble plate 13 is mounted-on the shaft 2 and rotates at the same speed as a driven shaft 2 thereby producing an oscillation of the end bearing ring 15 the frequency of which oscillation corresponds to the difference between the speed of drive shaft 1 and that of the driven shaft 2. Since this speed difference may be large, bearing ring 15 is journalled by means of a bushing 18 on wobble plate 13 and further the space between ring 15 and wobble plate 13 is filled by an intermediate bearing disc or plate member 14 which is exposed on both sides to the hydraulic medium and serves as a friction reducing means. The wobble plate 13 is fixed by means of a transverse key or pin 19 on the driven shaft 2, both against rotation and sliding movement.

The driven shaft 2 is journalled in the driving shaft 1 by means of a bearing ring 10 which is in the same plane with the ball bearing 8, and the rotary cylinder block 4 is also journalled in a bearing ring 11 on the driven shaft 2. A stationary cylinder block is mounted in a supporting means 3 and attached by screws thereto. An end bearing ring member 22 for the rotary cylinder block 4 is held by means of an abutment roller 23 which is guided in a track slot 24 in supporting casing means 3 and moves along an are parallel to the shafts. The bearing ring member 22 thus does not rotate, but oscillates. Depending on the position of wobble plate 20 which is connected to shaft 2 for rotation therewith, member 22 performs a reciprocating movement of greater or lesser amplitude and the frequency of the reciprocation of ring member 22 and consequently the number of strokes of the associated pistons 39 thus corresponds to therotational Speed of the driven shaft 2.

If wobble plate 20 is set at right angles to the driving shaft 2, the oscillation amplitude of bearing ring member 22 becomes zero as does also the length of the stroke of pistons 39. This is the position of direct drive in which no motion of operating fluid in the piston spaces, that is in the cylinder chambers 40, can take place, so that'only mechanical coupling action prevails.

Since the relative speed between the bearing ring member 22 and wobble plate 20 can become very high an intermediate bearing or floating disc 21 is inserted in axial direction between ring member 22 and wobble plate 20. Disc 21 subdivides the relative surface speed of the members 20 and 22. A further intermediate bearing ring 25 serves the same purpose to subdivide the relative surface speed of engaging members between the hubs of the parts 20 and 22. The wobble plate 20 is held against rotation relatively to the driven shaft 2by a cross bolt 26 which, however, permits rocking of the wobble plate. 7

The driven shaft 2 is journalled by means of ball bearings 9 in a supporting means shownto be a cover plate 7 on the motor end of supporting means 3, and a journal bearing 12 in the stationary cylinder block 5 serves to further support the driven shaft 2. The driven shaft 2 is integral throughout and extends from the journal bearing in the plane of the bearing 8 of the rotary-cylinder block 4 back to the cover plate 7 Supporting-meansfi, 3

and 7 form, together with the bottom part 67, the casing of the machine. The driven shaft 2 is preferably made in one piece in order to support the tension, twisting and bending stresses to which it is subjected. Shaft 2 is supported by the journal bearing 12 in the motor cylinder block 5 which is secured to supporting means 3, thus supporting shaft 2 laterally against oscillation. The rotary cylinder block 4 has a cylinder head end plate or wall 27, and the stationary cylinder block 5 has a-similar end plate or wall 28. The end plates 27 and 28 have ports 41 through which the oil flows into and out of two arcuate transverse sickle-shaped conduits 97, 98 of a valve plate member 29 terminating in ports on the sealing faces of valve member 29 whereby the suction and pressure sides of the cylinders 40 and the passages 38 of pistons 39 are supplied with oil. The valve plate 29 has control edges 80, a, 80b, 800 which limit the arcuate transverse ports of conduits 97, 98 and open and close the ports 41 in the required cycle, since the dead center positions of the wobble plates 13 and 20 and of the valve plate 29 are always synchronized, and the masking surfaces of the valve plate 29 bounded by the edges 80, 80a, 80b, 80c correspond to the radial width of the ports-41 in the cylinder end plates 27 and 28.

In order to maintain the friction surfaces and the sealing surfaces of the valve plate 29 small with respect to the cylinder end plates 27 and 28, the Walls 41' of ports 41 are inclined in such a manner that they lead from the outwardly arranged hydraulic working chambers 40 to the inwardly arranged arcuate transverse ports 97, 98 in order to reduce the relative speed at the outer circumference of the valve plate 29. Working chambers 40 are formed in cylinder bores 4a between the recessed front faces of pistons 38 and plate 27, and in the cylinder bores 5a between the recessed front faces of pistons 39 and plate 28. Also, intermediate speed sealing rings 30 and 31 are provided, separated from each other by a distance or spacing ring 32. The sum of the hydraulic forces exerted on the semi-circular portions of the cylinder head end plates 27, 28 by the hydraulic pressure in the hydraulic working chambers 40 is slightly greater-than the sum of the hydraulic forces which act upon the bridge portions of the cylinder head and the other wall portions of the rotor and stator so that the valve plate 29 operates with minimum surface pressure and therefore with minimum friction on the cylinder end plates 27 and 28.

The ring 32 prevents the coupling valve plugs 33 from being impelled outwardly by centrifugal force. These valve plugs or cocks 33 have passages 34 and inthe position shown in Fig. l, passages. 34 connect the (pressure) arcuate transverse port 97 with the (suction) arcuate transverse port 98 in the valve plate 29. The illustrated position thus corresponds to the condition in which the hydraulic coupling between pump rotor 4 and motor stator 5 is ineffective.

The connecting rod 35 has a ball head 36 at the piston end and a ball head 37 at the ring end. A conduit in the form of a bore. 38 in the connecting rod 35 provides communication between the hydraulic working chamber 48 and the hydraulic pressure pockets 42 in rings 15 and 22. The hydraulic pressure pockets 42, Fig. 3, are connected by means of small passages 44 with the hydraulic pressure spaces 43, in the bearing discs 14 and 21, and any three hydraulic pressure spaces 43 in the intermediate bearing discs 14 and 21 have their active total surfaces as large as the cross section of any pressure pocket 42 in the bearing rings 15 and 22. Each hydraulic pressure space 43 may be larger if desired but the sum of their cross-sectional areas must be nearly equal to that of the cross sectional area of the associated pistons. Similarly the sum of all the cross sectional areas of the hydraulic pressure pockets 42, Fig. 3, must also be nearly equal to the sum of the cross sections of; the associated i pistons and workingv chambers. The

surfaces of contact between the connecting rod beating rings 15, 22 and the intermediate bearing discs 14, 21, and between the latter and the wobble plates "13, 20 are in this way practically relieved of pressure, and thus friction is therefore reduced to a minimum.

By means of connecting pins 46 and 47, a coupling link 45 mechanically connects the wobble plate 20 with a shifting ring 49. The shifting ring 49 rotates with the driven shaft 2, while a shifting ring 48 remains stationary. Between the shifting ring 48 and the shifting ring 49 there are arranged intermediate speed rings 59 which subdivide the relative sliding speed. Pins 51 on the shifting ring 48 engage a fork lever 52 for the actuation of the wobble plate 20.

The rotary cylinder block 4 has attached thereto a bevel gear 53 rotating therewith at the drive or input speed and this bevel gear 53 meshes with a bevel gear 54 driving a flywheel 55 of a centrifugal pump. A pressure chamber 56 of the centrifugal pump communicates by means of a conduit 101 (Fig. l) and a connecting duct 57 with a control valve 60, and through a connecting duct 58, with check valves 71 in the valve plate 29, and also by means of a connecting passage 59 with the interior of a bellows-type, diaphragm 61. The casing 184 of the valve 60 is formed with an inlet port 189 connected to conduit pipe 57 and to exhaust ports 191 communicating (not shown) with the suction side of the centrifugal pump 55.

A reciprocable valve member 72 is connected by a stem 159 to the left-hand side of the diaphragm 61. The reciprocable valve member 72 closes in its intermediate position as shown, two outlet conduits 65, 66 leading to cylinder chambers on the opposite sides of a piston 64 guided within a cylinder 62. When the driving speed increases or diminishes as the torque on the driven shaft varies, the speed of the input or driving shaft 1 will also vary and simultaneously the pressure in the pressure chamber 56 of the centrifugal pump will vary, so that the pressure variation will alter the length of the diaphragm 61 (a bellows, or corrugated tube) and thus the position of the control valve member 72 with respect to the inlet opening 189 and outlet openings 65, 66 of the control valve 60. The oil flowing through the connecting ducts 101, 57, will flow according to the position of the control Slide 72, through conduits 65 or 66 to the right or left-hand side of the piston 64 in the control cylinder 62 thereby moving the piston 64 to the left or to the right as viewed in Fig. 1, so that piston 64 moves piston rod 63 and the fork lever 52 and varies the inclination of the wobble plate 20 and thus controls the transmission ratio as required by the desired torque at the driven shaft, depending on the input torque and the input speed.

To hold the driving speed within prescribed or permissible limits, or to vary the drivenspeed, a compression spring 69 is provided acting against the pressure in the diaphragm 61. The compression in the spring 69 can be adjusted by any suitable means. in the illustrated embodiment this is accomplished by mechanical means and by a speed selector lever 70 which can be set to the desired driving speed and which actuates the fork lever 68 to adjust the spring 69 to the desired tension. 7

The centrifugal pump and the control assembly are arranged in the bottom part 67 of thecasing 3, 6, 7, 67 to which the suction side of the centrifugal pump is connected and in which an oil sump is provided. The controlling mechanism should not be over or under-controlled and should have suflicient damping and if necessary a restoring means. To prevent disturbances due to air inclusions or oil vapor, at the places where air locks may occur; for example, at the inner diameter of the axial conduit of the rotating valve p1ate 29, suitable vents or leak passages 99 may be provided.

To actuate the valve plug 33in the control valve plate member29, a coupling lever 74 maybe rocked about 15 to the left, Fig. 1, thereby shifting the slide sleeve 75 for the coupling operation to the right to an extent limited by a pin 76 in a slot 78. Sleeve 75 shifts a thrust rod 77 in a central bore 77a in the driven shaft 2 so that segments guided in a guide slot 79 and nonrotatably attached to the valve plug 33, are rotated about the axis of the valve plug 33 and turn the same 90 so that passages 34 no longer connect parts 97, 98 thereby interrupting communication between the pressure side and the suction side in the valve plate 29 through the passages 34. In this position the transmission is engaged.

A spring disc 81 inserted between the bearing plate 6 and the ball bearing 8, urges cylinder block 4 against the valve plate 29 and the latter against the cylinder block 5 thereby fixing the driven shaft 2 in its longitudinal position in the housing 3.

The hydraulic transmission of the present invention is mainly intended for use as a fluid drive for motor cars. Shaft l is directly coupled with the engine shaft, while shaft 2 is operatively connected with the wheels of the car. When the wobble plate 20 is turned to a position perpendicular to the axis of shafts 1 and 2, the pistons 39 of the hydraulic motor do not perform a stroke. The control valve 3'3, 34 is closed, and the conduits 97, 98 are not connected. Shaft 1 turns with cylinder block 4, and since no liquid can flow from the pump cylinders through the passages 41 of the "cylinder end plates 27, 28 and conduits 97, 98 to the cylinder chambers of cylinder block 5, wobble plate 13 of the driven shaft 2 is rotated. Consequently, the transmission ratio is 1:1.

If the car is driven uphill in the above described radial position of wobble plate 20, the torque required by driven shaft 2 is increased. This results in a reduction of the rotary speed of the coupled shafts 1 and 2, if the engine is under full load. The rotary speed of the centrifugal pump 55 drops, and the pressure in conduit 101 and in the compressible member 61 is reduced so that member 61 is compressed and places wobble plate 20 in an inclined position through the servo motor piston 64 and linkage 63, 52. In the inclined position of wobble plate 20, the pistons 39 of the motor 5 start a reciprocating movement so that the shaft 2 can deliver a greater torque at a lower rotary speed. The car moves at a reduced speed uphill. In a similar manner, the rotary speed of shaft 2 is increased during a downhill drive.

Similar to the manner in which the wobble plate 20 is displaceably mounted on cross bolt 26, the wobble plate 13 can be mounted on a pivot bolt so that wobble plate 13 could be placed in a position perpendicular to the axis of shaft 1 whereby the transmission could be started with zero torque. The actuation of a wobble plate which can be displaced in this manner may be similar to that for the wobble plate 20. A pivoted wobble plate 13 can also be 'operatively connected to plate 20 for being displaced in dependency on the oblique position of the plate 20 by providing mechanical rod connections arranged in a longitudinal bore in the driven shaft 2. The non-displaceable wobble plate 13 on the illustrated embodiment can be dynamically weighted to eifect dynamic balance of the displaceable wobble plate 20 for which purpose a further plate displaceable in direction opposite thereto may be provided, which for sake of simplicity of showing is not illustrated on the drawing.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of hydraulic transmissions dilfering from the types described above.

While the invention has been illustrated and described as embodied in a friction reducing arrangement for a wobble plate type hydraulic transmission, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention,

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A hydraulic pump and motor transmission comprising, in combination, supporting means; a pair of coaxial cylinder blocks, one of said cylinder blocks being mounted for rotation and the other of said cylinder blocks being fixedly mounted in said supporting means, each of said cylinder blocks being formed with a set of cylinder bores, and having an inner end wall bounding said cylinder bores, each end wall having a face forming the inner end face of the respective cylinder block, each of said end walls being formed with a set of passages respectively associated with the respective cylinder bores, said passages terminating on one end in a set of first ports opening into the associated cylinder bores, and terminating at the other end in a set of second ports opening on said inner end faces, respectively, said second ports being arranged along a circle of smaller diameter and said first ports being arranged along a circle of greater diameter so that said passages are inclined to the axis of said cylinder blocks, each cylinder block having a central opening; piston means including a piston in each of said cylinder bores and a piston rod, said pistons forming in the associated cylinder bores working chambers communicating with said ports; drive shaft means connected to said rotatable cylinder block and passing through said central openings of said cylinder blocks; a valve member secured to said shaft means for rotation therewith and being located between said confronting inner end faces and having circular sealing faces having an area smaller than said inner end faces and slidably engaging the same, said valve member being formed with conduits passing therethrough and terminating on said sealing faces in third ports arranged in a circle having said smaller diameter, said third ports cooperating with said second ports of said end walls during relative turning movement between said valve member and cylinder blocks whereby the frictional torque between said valve member and said cylinder blocks is reduced; a pair of wobble plate means secured to said shaft means for rotation therewith, said wobble plate means being located on opposite sides of said pair of cylinder blocks and having bearing surfaces facing toward the same; and a pair of bearing members mounted on said wobble plate means, respectively, for rotation relative thereto and having bearing surfaces slidably engaged by said bearing surfaces of said wobble plate means, said bearing member supporting, respectively, the free ends of said piston rods; said pistons, piston rods and bearing members being formed with passages connecting the pair of cooperating bearing surfaces between each wobble plate means and each bearing member to said working chambers, each passage terminating in a pressure chamber partly bounded by an area of the bearing surface of the associated wobble plate means, the total area of said areas being substantially equal to the total cross-sectional area of said working chambers so that fluid communication is established between said pairs of bearing surfaces through said passages, said working chambers and said conduits in said valve member and so that the fluid pressure produced in said working chambers acts in opposite directions on said wobble plate means and is taken up by the portion of said shaft means located between said wobble plate means whereby the friction between said bearing surfaces and said inner end faces and sealing faces is reduced.

2. A hydraulic pump and motor transmission comprising, in combination, supportingmeans; a pair of coaxial cylinder blocks, one of said cylinder blocks being mounted for rotation and'the other of said cylinder blocks being fixedly mounted in said supporting means, each of said cylinder blocks being formed with a set of cylinder bores, and having an inner end wall bounding said cylinder bores, each end wall having a face forming the inner end face of the respective cylinder block, each of said end walls being formed with a set of passages respectively associated with the respective cylinder bores, said passages terminating on one end in a set of first ports opening into the associated cylinder bores, and terminating at the other end in a set of second ports opening on said inner end faces, respectively, said second ports being arranged along a circle of smaller diameter and said first ports being arranged along a circle of greater diameter so that said passages are inclined to the axis of said cylinder blocks, each cylinder block having a central opening; piston means including a piston in each of said cylinder bores and a piston rod, said pistons forming in the associated cylinder bores working chambers communicating with said ports; drive shaft means connected to said rotatable cylinder block and passing through said central openings of said cylinder blocks; a valve member secured to said shaft means for rotation therewith and being located between said confronting inner end faces and having circular sealing faces having an area smaller than said inner end faces and slidably engaging the same, said valve member being formed with conduits passing therethrough and terminating on said sealing faces in third ports arranged in a circle having said smaller diameter, said third ports cooperating with said second ports of said end walls during relative turning movement between said valve member and cylinder blocks whereby the frictional torque between said valve member and said cylinder blocks is reduced; a pair of wobble plate means secured to said shaft means for rotation therewith, said wobble plate means being located on opposite sides of said pair of cylinder blocks and having bearing surfaces facing toward the same; and a pair of bearing members mounted on said wobble plate means respectively, for rotation relative thereto and having bearing surfaces slidably engaged by said bearing surfaces of said wobble plate means, said bearing member supporting, respectively, the free ends of said piston rods; said pistons, piston rods and bearing member being formed with passages connecting the pair of cooperating bearing surfaces between each wobble plate means and each bearing member to said working chambers so that fiuid communication is established between said pairs of bearing surfaces through said passages, said working chambers and said conduits in said valve member and so that the fluid pressure produced in said working chambers acts in opposite directions on said wobble plate means and is taken up by the portion of said shaft means located between said wobble plate means whereby the friction between said bearing surfaces and said inner end faces and sealing faces is reduced.

3. A hydraulic pump and motor transmission comprising, in combination, supporting means; a pair of coaxial cylinder blocks, one of said cylinder blocks being mounted for rotation and for axial movement in said supporting means, and the other of said cylinder blocks being fixedly mounted in said supporting means, each of said cylinder blocks being formed with a set of cylinder bores, and having an inner end wall bounding said cylinder bores, each end wall having a face forming the inner end face of the respective cylinder block, each of said end walls being formed with a set of passages respectively associated with the respective cylinder bores, said passages terminating on one end in a set of first ports opening into the associated cylinder bores, and terminating at the other end in a set ofseoond ports opening on said inner end faces, respectively, said second ports being arranged along a circle of smaller diameter and said first portsbeing arranged along a circle of greater diameter so that saidpassages are-inclined to the axis of said cylinder blocks, each cylinder block having a central opening; piston means including a piston in each of said cylinder bores and a piston rod, said pistons forming in the associated cylinder bores working chambers communicating with said ports; drive shaft means connected to said rotatable cylinder block and passing through said central openings of said cylinder blocks; a valve member secured to said shaft means for rotation therewith and being located between said confronting inner end faces and having circular sealing faces having an area smaller than said inner end faces and slidably engaging the same, said valve member being formed with conduits passing therethrough and terminating on said sealing faces in third ports arranged in a circle having said smaller diameter, said third ports cooperating with said second ports of said end walls during relative turning movement between said valve member and cylinder blocks whereby the frictional torque between said valve member and said cylinder blocks is reduced; spring means abutting on said supporting means for urging a rotary cylinder block in axial direction toward said valve memher and urging said inner end face of said rotary cylinder block against the associated sealing face of said valve member; a pair of wobble plate means secured to said shaft means for rotation therewith, said wobble plate means being located on opposite sides of said pair of cylinder blocks and having bearing surfaces facing toward the same; and a pair of bearing members mounted on said wobble plate means, respectively, for rotation relative thereto and having bearing surfaces slidably engaged by said bearing surfaces of said wobble plate means, said bearing member supporting, respectively, the free ends of said piston rods.

4. A hydraulic pump and motor transmission comprising, in combination, supporting means; a pair of coaxial cylinder blocks, one of said cylinder blocks being mounted for rotation and for axial movement in said supporting means, and the other of said cylinder blocks being fixedly mounted in said supporting means, each of said cylinder blocks being formed with a set of cylinder bores, and having an inner end wall bounding said cylinder bores, each end wall having a face forming the inner end face of the respective cylinder block, each of said end walls being formed with a set of passages respectively associated with the respective cylinder bores, said passages terminating on one end in a set of first ports opening into the associated cylinder bores, and terminating at the other end in a set of second ports opening on said inner end faces, respectively, said second ports being arranged along a circle of smaller diameter and said first ports being arranged along a circle of greater diameter so that said passages are inclined to the axis of said cylinder blocks, each cylinder block having a central opening; piston means including a'piston in each of said cylinder bores and a piston rod, said pistons forming in the associated cylinder bores working chambers communicating with said ports; drive shaft means connected to said rotatable cylinder block and passing through said central openings of said cylinder blocks; a valve member secured to said shaft means for rotation therewith and being located between said confronting inner end faces and having circular sealing faces having an areasmaller than said inner end faces and slidably engaging the same, said valve member being formed with conduits passing therethrough and terminating on said sealing faces in third ports arranged in a circle having said smaller diameter, said third ports cooperating with said second ports of said end walls during relative turning movement between said valve member and cylinder blocks whereby the frictional torque between said valve member and said cylinder blocks is reduced; spring means abutting on said supporting means for urging a rotary cylinder block in axial direction toward said valve member and urging said inner end face of said rotary cylinder block against the associated sealing face of said valve member; a pair of wobble plate means secured to said shaft means for rotation therewith, said wobble plate means being located on opposite sides of said pair of cylinder blocks and having bearing surfaces facing toward the same; and a pair of bearing members mounted on said wobble plate means, respectively, for rotation relative thereto and having bearing surfaces slidably engaged by said bearing surfaces of said wobble plate means, said bearing member supporting, respectively, the free ends of said piston rods; said pistons, piston rods and bearing members being formed with passages connecting the pair of cooperating bearing surfaces between each Wobble plate means and each bearing member to said working chambers so that fluid communication is established between said pairs of bearing surfaces through said passages, said working chambers and said conduits in said valve member and so that the fluid pressure produced in said working chambers acts in opposite directions on said wobble plate means and is taken up by the portion of said shaft means located between said wobble plate means whereby the friction between said bearing surfaces and said inner end faces and sealing faces is reduced.

5. A hydraulic pump and motor transmission comprising, in combination, supporting means; a pair of coaxial cylinder blocks, one of said cylinder blocks being mounted for rotation and the other of said cylinder blocks being fixedly mounted in said supporting means, each of said cylinder blocks being formed with a set of cylinder bores, and having an inner end wall bounding said cylinder bores, each end wall having a face forming the inner end face of the respective cylinder block, each of said end walls being formed with a set of passages respectively associated with the respective cylinder bores, said passages terminating on one end in a set of first ports opening into the associated cylinder bores, and terminating at the other end in a set of second ports opening on said inner end faces, respectively, said second ports being arranged along a circle of smaller diameter and said first ports being arranged along a circle of greater diameter so that said passages are inclined to the axis of said cylinder blocks, each cylinder block having a central opening; piston means including a piston in each of said cylinder bores and a piston rod, said pistons forming in the associated cylinder bores working chambers communicating with said ports; drive shaft means connected to said rotatable cylinder block and passing through said central openings of said cylinder blocks; a valve member secured to said shaft means for rotation therewith and being located between said confronting inner end faces and having circular sealing faces slidably engaging said inner end faces and having an area smaller than the same, said valve member being formed with two conduits passing therethrough and terminating on said sealing faces in third ports arranged in a circle having said smaller diameter, said third ports cooperating with said second ports of said end walls during relative turning movement between said valve member and cylinder blocks whereby the frictional torque between said valve member and said cylinder blocks is reduced, said valve member being formed with a passage connecting said two conduits therein; control valve means located in said passage and being movable between an open position for connecting said two conduits, and a closed position; means connected to said control valve means for moving the same between said positions thereof; a pair of wobble plate means secured to said shaft meansfor rotation therewith, said wobble plate means being located on opposite sides of said pair of cylinder blocks and having bearing surfaces facing toward the same; and a pair of bearing members mounted on said wobble plate means, respectively, for rotation relative thereto and having hearing surfaces slidably engaged by said bearing surfaces of said wobble plate means, said bearing member supporting, respectively, the free ends of said piston rods; said pistons, piston rods and bearing members being formed with passages connecting the pair of cooperating bearing surfaces between each wobble plate means and each bearing member to said working chambers so that fluid communication is established between said pairs of hearing surfaces through said passages, said working chambers and said conduits in said valve member and so that the fluid pressure produced in said working chambers acts in opposite directions on said wobble plate means and is taken up by the portion of said shaft means located between said wobble plate means whereby the friction between said bearing surfaces and said inner end faces and sealing faces is reduced.

6. In a rotary pump and motor transmission including a wobble plate type pump device and a wobble plate type hydraulic motor device, in combination, a pair of coaxial cylinder blocks, one of said coaxial cylinder blocks being mounted for rotation, and the other of said cylinder blocks being stationary, said cylinder blocks having opposite parallel end faces, each of said cylinder blocks being formed with a set of cylinder bores opening on said end faces in a set of cylinder ports, said sets of cylinder ports being arranged along two circles having the same diameter and having the centers thereof located in the axis of said cylinder blocks; wobble plate means located on opposite sides of said cylinder block means; drive shaft means for driving said rotatable cylinder block and said wobble plate means; a pair of end plates each having two faces, each end plate being fixedly secured to one of said cylinder blocks and having one of said faces abutting against the respective end face of the associated cylinder block, each of said end plates being formed with a set of passages therethrough, each of said passages opening on said one face in a first port, said first ports being arranged in a circle having substantially the same diameter as said first-mentioned circle so that said first ports communicate with said cylinder ports, said passages opening on the other face of the respective end plate in a set of second ports arranged in a smaller circle having a diameter smaller than the diameter of said first-mentioned circle so that said passages extend through said end plates at an angle to the axis of said cylinder blocks; and a rotary valve member driven by said shaft means arranged between said end plates and having sealing faces abutting against said other faces of said end plates, said valve member being formed with conduits passing therethrough and opening on said sealing faces in arcuate ports having substantially the same diameter as said smaller circle so that said second ports of said two end plates communicate through said conduits in said valve member.

7. In a rotary pump and motor transmission including a wobble plate type hydraulic pump device and a wobble plate type hydraulic motor device, each of said devices having a cylinder block and piston means therein, incombination, an output shaft; a pair of wobble plates respectively associated with said pump device and said hydraulic motor device and connected to the respective piston means, said wobble plates being mounted on said output shaft and being connected to the same for rotation therewith, the one wobble plate which is associated with said hydraulic motor device being mounted on said output shaft movable between a plurality of operative positions located in a plane inclined to the axis of said output shaft and an inoperative position locatedin a. plane perpendicular to said output shaft, said one wobble plate being adapted to operate the associated hydraulic motor device only in said operative positions thereof; operating means connected to said one wobble platefor moving the same between said inoperative and operative positions; an input shaft for driving said hydraulic pump device; a centrifugal pump means driven from said input shaft and including a pressure conduit means, said centrifugal pump means being adapted to produce in said pressure conduit means a fluid pressure corresponding to the rotary speed of said input shaft; pressure responsive fluid operated means including a bellows-type diaphragm defining a pressure chamber communicating with said pressure conduit means and being movable between a plurality of positions in accordance with the pressure in said pressure conduit means, a control valve operated by said bellows-type diaphragm, and servo-motor means actuated by said control valve, said servo-motor means being connected to said operating means for moving said one wobble plate between said ino erative and operative positions whereby the capacity of the hydraulic motor device associated with said one wobble plate is adjusted in accordance with the speed of said input shaft.

8. In a rotary pump and motor transmission, in combination, a wobble plate type hydraulic pump device and a wobble plate type hydraulic motor device, each of said devices having a cylinder block and piston means therein, each of said hydraulic devices including a wobble plate connected to the respective piston means; conduit means hydraulically connecting said devices; an output shaft sup porting said wobble plates and being connected to the same for rotation, the one wobble plate which is associated with said hydraulic motor device being mounted on said output shaft movable between a plurality of operative positions located in a plane inclined to the axis of said output shaft and an inoperative position located in a plane perpendicular to said output shaft, said one wobble plate being adapted to operate the associated hydraulic motor device only in said operative positions thereof; operating means connected to said one wobble plate for moving the same between said inoperative and operative positions; an input shaft connected to said hydraulic pump device for driving said hydraulic pump device; a centrifugal pump means driven from said hydraulic pump device and including a pressure conduit means, said centrifugal pump means being adapted to produce in said pressure conduit means a fluid pressure corresponding to the rotary speed of said input shaft; pressure responsive fluid operated means including a bellows-type diaphragm defining a pressure chamber communicating with said pressure conduit means and being movable between a plurality of positions in accordance with the pressure in said pressure conduit means, a control valve operated by said bellows-type diaphragm, and servo-motor means actuated by said control valve, said servo-motor means being connected to said operating means for moving said one wobble plate between said inoperative and operative positions, whereby the capacity of the hydraulic motor device associated with said one wobble plate is adjusted in accordance with the speed of said input shaft.

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